Die casting machine



June 10, 1958 L. RING 2,837,792

DIE CASTING MACHINE 4 Sheets-Sheet 1 Fuga sept. 24. 1953 June 1o, 195s L. RING 2,837,792

DIE CASTING MACHINE Filed Sept. 24, 1953 4 Sheets-Sheet 2 INVENToR.

UC/HA/ R/A/G ATTORNEYS June 1o, 195s L. RING DIE CASTING MAGHINE Filed Sept. 24. 1953 INVENTOR.

ac/AN R/A/G 4 Sheets-Sheet 3 ,2S/Www I June1o,195s L RING 2,837,792

DIE CASTING MACQINE 4 Sheets-Sheet 4 Filed sept. 24, 1953 United States DIE CASTING MACHINE Lucian Ring, Detroit, Mich., assigner to Ring Aluminum Development Company, a corporation of Michigan Application September 24, 1953, Serial No. 332,679

Claims. (Cl. 22-68) This invention relates generally to die casting equipment `and refers more particularly to improvements in apparatus of the type employed in die casting lightweight non-ferrous metals such, for example, as aluminum and magnesium.

it is `an object of this invention to simplify as well as greatly expedite the manufacture of die -castings on a high volume production basis by substantially reducing the time required to transfer molten metal from a source of supply to the interior of the injection clyinder in advance of the plunger in said cylinder.

lt is another object of this invention to provide die casting apparatus of the above type wherein provis-ion is made for sealing the cylinder from the atmosphere during retracting. movement of the plunger in said cylinder in order to produce a sub-atmospheric pressure in the cylinder in advance of the plunger suiiicient to draw the required quantity yof molten metal into the cylinder through an intake port formed in the cylinder in a position to be uncovered by the plunger just prior to movement of the latter to its retracted position.

It is still another object yof this invention to feed molten metal from a container into the injection cylinder through a supply tube having the receiving end immersed within a supply of molten metal and having the discharge end engageable with an annular seat surrounding an intake port in the injection cylinder. Thus, the supply tube is maintained at a temperature approximating the temperature of the molten metal and solidiiication of molten metal within the tube during the feeding phase of the die casting operation is material-ly reduced.

It is a further object of this invention to provide a structure of the type set `forth in the preceding paragraph wherein the discharge end of the supply` tube is normally maintained out `of contact with the annular seat on the injection cylinder and is engaged with the annular seat only `during the metal Afeeding phase of the die cast-ing cycle. Thus, there is less tendency for the relatively cool injection cylinder to` reduce the temperature oi the supply tube to such an extent that molten metal solidiiies in the tube during the feeding operation.

lt is a still further object of this invention to provide means operable in timed relationship to reciprocation of the plunger -in the injection cylinder for moving the supply tube into and out of contact with the annular seat on the cylinder while maintaining the receiving end of the tube immersed in the supply of molten metal.

lt is another feature of this invention to provide means responsive to movement of the plunger toward its retracted position within the injection cylinder for sealing the discharge end of the cylinder and thereby produce a sub-atmospheric pressure in the cylinder at the outer end of the plunger sutiicient to draw molten metal into the cylinder through the supply tube.

The foregoing as well as other objects will be made more apparent as this description proceeds especially when considered in connection with the accompanying drawings, wherein 2,837,792 Patented June 1), 1958 Figure 1 is a side elevational view partly in section of die casting apparatus constructed in accordance with this invention;

Figure 2 is a cross sectional View taken on the line 2 2 of Figure 1;

Figure 3 is a cross sectional View taken on the line 3 3 oFigure l;

Figure 4- is a sectional View taken substantially on the line 4 4 of Figure 3 Figure 5 is a cross sectional view taken on the line 5 5 of Figure 4;

Figure 6 is a sectional View taken on the line 6 6 of Figure 2;

Figure 7 is a cross sectional view taken on the line 7 7 of Figure 6;

Figure 8 is a cross sectional view taken on the line 8 8 of Figure 6;

Figure 9 is a cross sectional view taken on the line 9 9 of Figure l;

Figure l0 is a sectional View taken on the line l6 16} of Figure 5 Figure l1l is an enlarged sectional View taken on line Il ll of Figure l;

Figure l2 is a iiow diagram of a part of the apparatus;

Figure 13 is a sectional view taken on the line 13 13 of Figure 11; and

Figure 14 is a semi-diagrammatic elevational View of a part of the apparatus shown in Figure 1.

in Figure l of the drawing, the numeral Ztl designates a typical die structure having .a stationary part 2i and a movable part 22. The part 21 is suitably iixed to a frame member 23 and the part 22 is supported at the outer side of the part Z1 for movement toward and away from the latter part. The adjacent surfaces of the die parts are yfashioned to form a cavity 24 in the closed position of the die and to provide a passage 25 leading into the cavity 24.

The part 22 is secured -to the inner end of an annular housing 26 having the outer end mounted on a slide 27. The slide 27 is mounted on guide bars 2S having the inner ends secured to the frame member 23. Any suitable means not shown herein may be used for moving the slide 27 in opposite directions along the guides Z3 to open and close the die 20.

Mounted within the housing 26 is an ejector plate 29 having pins 30 extending inwardly from the plate 29 through bores formed in the -die part 22 and registering with the die cavity 24. The plate 29 is actuated to eject the casting from the die cavity by a rack bar 31 and pinion 32. The bar 31 is secured to the plate 2% at the outer side of the latter and meshes with the pinion 32 which is driven by any suitable means not shown herein.

l'violten met-al is introduced into the die cavity 24 through an injection cylinder 33 having the outer end projecting through aligne-d openings in the frame member 23 and fixed die part 21, as shown in Figures 1 and 4 of the drawings. The outer end of the cylinder 33 is open and communicates with the die cavity 24 through the medium of the passage 2-5. The open outer end of the cylin-der 33 may be closed by a cylindrical plug 34 slidably supported within a bore formed in the movable die part ZZ and having an annular tapered seat 35 at the inner end engageable with an annular tapered seat 36 surrounding the open end of the cylinder 33. The angle of taper of the seats 35 and 36 is preferably somewhat different in order to assure a iluid tight seal between said seats when in contact.

As shown in Figure 1 of the drawings, the plug 34 is reduced at its outer end and projects axially through the movable die 22 for connection to the inner end of a lubricant supply tube 37. The tube 37 projects outwardly through 4an opening in the center of the plate 29 and is slidably supported by a bushing 33. The inner end of the tube 37 communicates with fluid passages formed in the plug 34 in a manner to lubricate the walls of the bore formed in t-he die part 22 and the outer end of the tube is connected in any suitable manner to a source of lubricant supply. In this connection, it is to be noted that the bore in the movable die part Z2 within which the plug 34 is slidably supported is vented to the atmosphere by a passage 39 formed in the movable die part 22. The purpose of the passage 39 is to prevent a pressure from building up at the outer side of the plug 34 during outward movement of the plug relative to the movable die part 22. In addition, it is to be noted that the outer end of the reduced portion of the plug provides a shoulder 40 which is engageable by the ejector plate 29 as the latter is moved inwardly to eject a casting from the cavity 24. The arrangement is such that the plug 34 is moved axially inwardly into sealing engagement with the open outer end of the cylinder 33 by the ejector plate 29 when the latter is operated to eject a casting from the die cavity 24. ln any case the plug 34 closes the outer end of the cylinder 33 when the die is opened and renders it possible to produce a vacuum within the cylinder 33, as will be presently described.

The inner end of the cylinder 33 is supported in a block 4l which is shown in Figure 3 of the drawings as formed' with a vertically elongated opening 42 therethrough for receiving the cylinder 33. The lower end of the opening 4Z is shaped to provide an extended bearing contact with the adjacent outer surfaces of the cylinder 33 and the latter surfaces are maintained in contact with the block by set screws 43 threadably supported in the block at the top of the latter in positions to extend into the upper end of the opening 42 .and engage the cylinder 33. The bottom of the block 41 is slotted or cut away to provide a clearance opening 44 directly opposite an intake port 45 formed in the cylinder 33 at the bottom of the latter. The arrangement is such that the intake port 45 is accessible for connection to a source of molten metal supply whch will be more fully hereinafter describede Mounted within the cylinder 33 is a plunger 46 having an enlarged head 47 at the outer end of a size to slidably engage the inner surface of the cylinder 33. As shown in Figures 6-8 inclusive of the drawings, the inner end of the plunger 46 is supported by a bearing block 4S having a recess 49 which is open at the top to freely receive the inner end of the plunger 46 and a clamping member 50. The portion of the recess 49 at the outer end of the block 43 is shaped to form a saddle 51 for supporting the inner end of the plunger 46, and the clamping member Stb assumes a position in the recess 49 at the inner end of the plunger 46. An annular enlargement 52 is formed on the inner `end of the plunger 46 and abuts a shoulder 53 formed on the bearing block f3 to prevent outward axial displacement of the plunger 46 relative to the bearing block 43. Inward axial displacement of the plunger 46 relative to the bearing block 43 is prevented by the clamping member t) which is secured in the recess 49 of the bearing block by a stud 53. VJpward displacement of the inner end of the plunger 46 relative to the bearing block 48 is prevented by a rib 54 formed on the outer face of the clamping member Sti in a position to engage the top of the enlargement 52, as shown in Figures 6 and 8 of the drawings. The above construction is such that the inner end of the plunger 46 is readily removably secured to the bearing block 43.

The bearing' block 48 also serves as a coupling for connecting the inner end of the plunger 46 to a 'hydraulic motor 55'. The hydraulic motor 55 comprises a cylinder 56 and a piston 57 slidably supported Within the cylinder 56. As shown in Figure 1 of the drawings, the outer end of the cylinder 56 is secured to asuitable support 5S and the piston 57 is connected to a rod 59 which projects outwardly through the outer end of the cylinder 56. The outer end of the rod 59 is secured to the bearing block 48V in a manner such that movement of the pist-on 57 in the cylinder 56 imparts a corresponding movement to the plunger 46.

As shown in Figure 12 of the drawings, the piston 57 is actuated by a hydraulic fluid medium contained in a reservoir 60 and circulated by a pump 61. The intake side of the pump 61 is connected to the reservoir by a conduit 62 and the discharge side of the pump is connected to a four-way valve 63. The valve 63 is also connected to opposite ends of the cylinder 56 and to the reservoir 69 in a manner such that movement of the valve to its dierent positions alternately connects opposite ends l f the cylinder 56 to the pump and reservoir. ln the present instance, the four-way valve 63 is normally urged by a spring (not shown) to a position wherein the inner end of the cylinder 55 is connected to the pump 61 and wherein the outer end of the cylinder 55 is connected to the reservoir so that normally the injection plunger 46 is in its outermost position adjacent the closure plug 34. Movement of t-he four-way valve 63 to its other position against the action of the spring (not shown) is accomplished by a solenoid 63 which is electrically connected to a timer T. The timer T is connected in an electric circuit with a limit switch S positioned for operation to close the circuit to the timer T by an abutment 27' movable with the slide 27.

It follows from the foregoing that as the slide 27 is moved inwardly to close the die 20, the limit switch S is Operated by the abutment 27 to close the circuit to the timer T which in turn closes the circuit to the solenoid 63 and operates the valve 63 to introduced fluid under pressure into the outer end of the cylinder 55 and exhaust fluid under pressure from the inner end of thc cylinder S5. Thus the piston 57 in the cylinder 55 is moved inwardly and a corresponding movement is imparted to the plunger 46 in the injection cylinder 33. It will be noted that inward movement of the plunger from its outermost position produces a sub-atmospheric pressure within the outer end of the cylinder 33. In other words, a suction is created within the cylinder 33 which serves to draw the closure plug 34 into fluid tight sealing contact with the annular seat 36 surrounding the open outer end of the cylinder 33. Thus, airis prevented from escaping into the cylinder 33 through the open outer end thereof during the retracting movement of the plunger 46 and the resulting drop in pressure within the cylinder 33 at the outer side of the plunger 46 is sucient to produce the suction required to draw molten metal upwardly through the intake port 45 when the latter is uncovered by the plunger 46, or in other Words, when the plunger 46 is in its retracted position shown in Figure 4 of the drawings.

The Volume or quantity Iof molten metal drawn upwardly through the intake port 45 into the cylinder 33 may be controlled by varying the extent of pressure drop within the cylinder 33. This can be accomplished by regulating the rate of retraction of the plunger 46 and/ or by providing relief areas in the sealing plug 34 so as to allow a limited amount of lair to escape into the cylinder 33 during retraction of the plunger 46.

When the desired amount of molten metal is drawn into the injection cylinder 33 at the outer side of the plunger 46, the timer T opens the circuit to the solenoid 63 and enables the valve 63 to move to a position wherein uid under pressure is introduced into the inner end of the cylinder 55 and is exhausted from the outer end of the cylinder 55. Hence, the piston 57 is moved outwardly and a corresponding movement is imparted to the plunger 46 by the connecting rod 59 between the plunger and the piston 57. During initial outward movement of the plunger 46 the intake port 45 is closed and the closure plug 34 is forced outwardly to a position wherein the inner surface thereof forms in effect a wall of the passage 25 in the die 20. Hence, molten metal is displaced through the o pen outer end of the cylinder 33 and 'but are inclined with respect to thecylinder axis to such an extent that the ends of adjacent passages communicate with one another and provide in eiect a single circuitous passage. Water or some other cooling medium is circulated through the passages and for accomplishing this result intake and outlet conduits and 66 are respectively connected to opposite ends of the circuitous passage formed by the passages 64. In addition to the above cooling arrangement, the cylinder 33 has diametrically opposed bores 67 extending axially outwardly from the inner end of the cylinder and connected to outlet conduits 68, as shown in Figure 4 of the drawings. Extending axially into each of the bores 67 from the inner end of the cylinder 33 is a tube 69 having a diameter substantially less than the diameter of the bores 67 to provide 'a jacket for a cooling medium Within the bores 67. The inner ends of the tubes 69 are respectively connected to intake conduits 70 which in turn communicate with a source of cooling medium supply, not shown herein. Thus, it will be seen that the cylinder 33 is etfectively cooled and is maintained at a more or less uniform temperature throughout the operation of the apparatus.

As shown in Figures 4 and 6 of the drawings the plunger 46 has a bore 7l which extends axially of the plunger from the inner end of the latter and is'divided into two communicating passages 72 by a partition 73. Referring now to Figure 2 of the drawings, it will be noted that one passage '72 communicates with an intake conduit 74 for cooling medium under pressure, and the other passage 72 communicates with an outlet conduit 75 for the cooling medium. Consequently, the cooling medium is circulated axially of the plunger 46 and the latter is also maintained at a substantially uniform temperature during the casting operation.

Provision is also made herein for lubricating the inner surface of the cylinder 33 during operation of the plunger .Y

46. For accomplishing this result, the plunger 46 is formed with an axially extending lubricant passage 76. The inner end of the passage 76 is connected to a source of lubricant supply by a conduit 77 and the outer end of the passage communicates with the interior of the 51,

cylinder 33 at the inner side of the head 47 on the plunger 46 through ports 7S.

In the present instance, the lubricant supply conduit 77 is connected to a lubricant supply cylinder 7 9throug'n a control valve 86 and a regulating valve 81 by a conduit 82, as Shown in Figure 14 of the drawings. The cylinder k79 contains lubricant under pressure so that opening of the valve Sii causes lubricant to flow into the cylinder 33 through the passage 7 6 in the plunger 46 at a rate depend ing upon the adjustment of the valve 81. The valve 80 is operated to supply lubricant to the cylinder 33 each time the die 29 is closed and is'actuated by a roller S3 mounted on the slide 27. Ilf desired, the lubricant supply tube 37 for the closure plug 34 may also be connected to the conduit S2 so that a supply of lubricant is introduced into the bore in the die part 22 each time the die is closed.

It has previously been stated that when the plunger 46 has been retracted to its innermost position shown in -Figure 4 of the drawings, ymolten metal is drawn upwardly into the cylinder 33 throughy the intake port 45 by the suction produced in the cylinder during retracting movement of the plunger 46. As shown in Figure ll of the drawings, the molten metal is housed in a container 84 which is supported directly below the intake port 45 in the cylinder 33 and is open at the top. Molten metal is conducted from the container 34 to the intake port 4S by a vertically extending tube 85 having the lower end immersed in the molten metal in the container and having the upper end projecting above the level of the molten metal in direct vertical alignment with the intake port 45. The supply tube has ya portion 88 adjacent the upper end reduced in diameter for attachment to a supporting member 86 positioned directly below the bearing block 41. As shown in Figure 13 of the drawings, the opposite sides 89 of the reduced portion 88 are flattened to enable inserting the reduced portion into a narrow slot 87 formed in the supporting member 86 and extending inwardly from one edge of the member 86. The slot '87 terminates in an enlarged portion which enables rotating the tube 85 to lock the same in assembled relationship with the supporting member 86.

The supporting member 86 is connected by vertical rods 99 to a cross bar 91 positioned above the bearing block 41. The vertical rods 9@ are respectively slidably supported in vertical grooves 92 formed in the bearing block 41 at opposite sides thereof and the upper ends of the rods 9i) are reduced to extend through openings formed in the bar 91. The upper extremities of the reduced portions of the rods 99 are threaded and abutments 93 are respectively secured to the upper extremities of the rods. Coil springs 94 are respectively mounted on the rods 99 between the abutments 93 and the cross bar 91. As will be presently described, the purpose of the springs 94 is to cushion engage-ment of the supply tube 85 with the cylinder 33 upon upward movement of the cross bar 91.

The cross bar 91 is connected to a hydraulic motor '95 comprising a vertically extending cylinder 96 and a piston 97 mounted in the cylinder for sliding movement. The piston 97 is connected to the cross bar 91 by a rod 92 so that vertical movement of the piston 97 in the cylinder 96 imparts a corresponding movement to the cross bar 9i and supply tube 8S. As shown in Figure l2 of the drawings, the opposite ends of the cylinder 96 are alternately connected to the reservoir 6d and the pump 6l by a four-way valve 9 9. In the present instance, the valve 99 is normally biased by a :spring (not shown) to a position wherein the upper end of the cylinder 96 is connected to the pump 6l and wherein the lower end of the cylinder 96 is connected to the reser- Voir. In other words, the valve 99 is normally in a position wherein the supply tube 85 is spaced downwardly from the injection cylinder 33. A solenoid 190 is provided tor moving the valve 99 to its other position wherein the lower end of the cylinder 96 is connected to the pump and the upper end of the cylinder 96 is connected to the reservoir 60 `with the result that the piston 97 in the `cylinder 96 is moved upwardly to engage the upper end of the supply tube f85 with the cylinder 33. The solenoid is energized simultaneously with the solenoid 63 by the limit switch S through a second timer T. As a result, closing of the limit switch S by movement of the slide 27 inwardly to close the die Z9 actuates both'the four-way valve 63 and 99 to respectively move the injection plunger 46 inwardly on its suction stroke and to raise the supply tube 85 into engagement with the injection cylinder 33.

As the tube 85 is moved upwardly by the hydraulic motor 95, the upper end thereof engages an annular seat lul formed 4on the cylinder 33 around the intake port 45 to establish communication between the interior of the ycylinder 33 and the molten metal within the container' 84. In this connection, it will be noted from Figure ll of the drawings that the cylinder is recessed as at 1li-l2 to provide clearance for receiving the upper extremity of the supply tube 85 and to also reduce the area of the intake port 4:5 exposed to molten metal ilowing from the vsupply tube to the interior of the cylinder 33. This structure is important in that the temperature of the cylinder 33 substantially lower than the temperature of the molten metal and by reducing the area of the intake port 45 exposed to the molten metal there is less opportunity for the molten'metal to become solidied within the intake port. i It is apparent from the foregoing that the `springs 94- function as a shock absorber and prevent the supply tube S5 from striking the seat lill on the cylinder. Also, the rate of upward movement of the supply tube 8S by the piston 97 in the cylinder 5"-5 may be regulated by an adjustable restriction in the conduit 99 in the form of a needle valve M3.

The lower end of the supply tube 85 remains immersed in the molten metal in the container 84 throughout movement of the tube into and out of engagement with the annular seat lill surrounding the intake port 45 so that the tube is maintained at approximately the temperature of the molten metal at all times, and solidification of molten metal within the tube is avoided. lnasmuch as the cylinder 33 is cooled to assure proper operation ot the plunger 46, there is a tendency for the supply tube 85 to become chilled when brought into contact with the cylinder 33, and in order to reduce such a tendency to a minimum provision is made herein for delaying contact of the upper end of the tube 85 with the seat 101 until the plunger 46 has been retracted to a position wherein the port d5 is about to be uncovered by the head i7 on the plunger. This delay is effected by adjustment of the valve 163, previously described as aiso operable to retard upward movement of the tube S5 and thereby avoid striking the cylinder 33 with the tube, Although it is desirable to delay contact of the tube 85 with the -cylinder 33 as long as possible, nevertheless, care must be taken to assure sealing engagement of the upper end of the tube 85 with the annular seat lill surrounding the intake port 45 before the latter is uncovered by the head 47 on the plunger i6 so that the full effect of the suction produced in the cylinder by retraction of the plunger is available for drawing molten metal into the cylinder.

It follows from the above that as soon as the intake port 45 in the injection cylinder 33 is uncovered by the head 47 of the plunger 46 during the inward movement of the latter, molten metal from the container 84 is drawn upwardly into the cylinder 33 at the outer side of the plunger head 47 by the suction created in the cylinder 33 during the inward or retracting movement of the plunger 46 in said cylinder. The timer T is set to assure maintaining the injection plunger 4o in its retracted position until the required amount of molten metal has been drawn into the cylinder 33 at the outer side of the plunger head 47. When the required amount of molten metal has been transferred from the container 84 to the interior of the cylinder 33 through the tube 35, the timer T opens the circuit to the solenoid 63' and permits movement of the four-way valve 63 to a position wherein the plunger 46 is moved by the piston 57 in an outward direction toward the die 2t?, or in other words, is moved in a direction to inject the molten metal into the die cavity 24. The timer T' maintains the solenoid litt) energized or maintains the valve 99 in a position wherein the tube 85 is raised into engagement with the cylinder 33 until the head 47 on the plunger 46 moves outwardly beyond the intake port 45 in the cylinder 33. When this is accomplished the timer T de-energizes the solenoid 100 and allows the valve 99 to be moved to a position wherein the piston 97 is moved downwardly in the cylinder 96 and the tube SS is lowered into the molten Vmetal in the container 84. Thus, the tube 85 is moved out of contact with the cylinder 33 shortly after the head 47 on the plunger 46 moves outwardly beyond the intake port 4S so that the length of time the tube 8S remains in contact with the relatively cool injection cylinder 33 is reduced to a minimum. Continued movement of the plunger 46 toward the die 20 forces the closure plug 34 to its retracted or open position with assz'rc 8 respect to the open end of the cylinder 33 and molten metal is displaced from the cylinder 33 into the cavity 24 through the passage 25 formed by the retracting movement of the plug 34.

What I claim as my invention is:

l. Die casting apparatus comprising a die having a cavity, a cylinder having a discharge opening communicatingrwith the said cavity and having an intake port for molten casting material spaced axially inwardly from saidV discharge opening, a plunger reciprocable axially within and relative to said cylinder, said plunger being movable outwardly relative to said cylinder to inject molten casting material from said cylinder into said cavity and movable inwardly relative to said cylinder to a position inwardly beyond said intake port, means providing a supply passage communicating with said intake port yand with a source of supply of molten casting material, means operative in response to initial inward movement of said plunger relative to said cylinder to close said discharge opening and keep it closed during the entire subsequent inward movement of said plunger, said last-named means cooperating with said plunger to provide a closed chamber in said cylinder which gradually increases in volume during inward movement of said plunger to produce a vacuum in said cylinder at the outer side of said plunger sucient to draw molten casting material through said supply passage into said cylinder when said plunger assumes a position inwardly beyond said intake port.

2. Die casting apparatus as dened in claim l in which said last-named means is operative in response to initial outward movement of said plunger relative to said cylinder to open said discharge opening and leave it open during the entire subsequent outward movement of said plunger.

3. Die casting apparatus as dened in claim 2 in which said supply passage is a closed passage having communication with said intake port and said source of supply only being otherwise imperforate.

4. Die casting apparatus comprising a die having a cavity, a cylinder having a discharge opening at the outer end communicating with said cavity and having an intake port for molten casting material spaced axially inwardly from said discharge opening, a plunger reciprocable axially within and relative to said cylinder, said plunger being movable outwardly relative to said cylinder to inject molten casting material from said cylinder into said cavity and movable inwardly relative to said cylinder to a position inwardly beyond said intake port, means providing a supply passage communicating with said intake port and with a source of supply of molten casting material, a plug supported outwardly of the outer end of said cylinder for sliding movement axially relative to said cylinder, said plug being moved axially inwardly relative to said cylinder in response to initial inward movement of said plunger relative to said cylinder to sealingly engage and close said discharge opening and keep it closed during the entire subsequent inward movement of said plunger, said plug cooperating with said plunger to providel a closed chamber in said cylinder` which gradually increases in volume during inward movement of said plunger to produce a vacuum in said cylinder at the outer side of said plunger sufficient to draw molten casting material through said supply passage into said cylinder when said plunger assumes a position inwardly beyond said intake port, said plug being moved axially outwardly relative to said cylinder in response to initial outward movement of said plunger relative to said cylinder to disengage and open said discharge opening and leave it open during the entire subsequent outward movement of said plunger.

v5. Die casting apparatus as defined in claim 4 in which said plug is mounted for free axial movement independently of any of said die structure, in which said plug is moved axially inwardly relative to said cylinder to close said discharge opening by vacuum in said cylinder produced by axially inward movement of said plunger, and in which said plug is moved axially outwardly relative to said cylinder to open said discharge opening by pressure in said cylinder produced by axially outward movement of said plunger.

6. Die casting apparatus as defined in claim in which said supply passage is a closed passage having communication with said intake port and said source of supply only and being otherwise imperforate.

7. Die casting apparatus comprising a die having a cavity, a cylinder havingl a discharge opening communicating with said cavity and having an intake port for molten casting material spaced axially inwardly from said discharge opening, a plunger reciprocable axially within and relative to said cylinder, said plunger being movable outwardly relative to said cylinder to inject molten casting material from said cylinder into said cavity and movable inwardly relative to said cylinder to a position inwardly beyond said intake port, means providing a supply passage communicating with said intake port and with a source of supply of molten casting material, means operated in timed relation to and during initial inward movement of said plunger relative to said cylinder to close said discharge opening and keep it closed during the entire subsequent inward movement of said plunger, said last-named means cooperating with said plunger to provide a closed chamber in said cylinder which gradually increases in volume during inward movement of said plunger to produce a vacuum in said cylinder at the outer side of said plunger suiicient to draw molten casting material through said supply passage into said cylinder when said plunger assumes a position inwardly beyond said intake port.

8. In die casting apparatus, a cylinder having a discharge opening and having an intake port spaced inwardly from said discharge opening axially of said cylinder, a plunger supported in said cylinder for axially inward sliding movement to a position at the inner side of said intake port and axially outward sliding movement outwardly beyond said intake port to expel molten casting material in said cylinder from said discharge opening, means providing a supply passage communicating with said intake port and with a supply of molten casting material, and means for closing said discharge openingduring movement of said plunger axially inwardly of saidcylinder to produce a sub-atmospheric pressure in said cylinder at the outer side of said plunger Y sucient to draw molten casting material through said supply passage into said cylinder through said intake port when the latter is uncovered by movement of said plunger to the inner side of said intake port.

9. Die casting apparatus comprising a die having a cavity, means for introducing molten casting material into said cavity including a cylinder having a discharge opening adapted to communicate with said cavity and having an intake port for molten casting material spaced inwardly from said discharge opening axially of said cylinder, a plunger supported in said cylinder for axially inward sliding movement to a position at the inner side of said intake port and axially outward sliding moveplunger to the inner side of said intake port.

10. In die casting apparatus, a cylinder having a discharge opening, a plunger supported in said cylinder for axial sliding movement in one direction toward said discharge opening to expel casting material in said cylinder from said discharge opening and in the opposite direction away from said discharge opening to a retracted position, said cylinder having an intake port between said discharge opening and said plunger in the retracted position of the latter, means providing a supply passage communicating with said intake port and with a supply of molten casting material, and means for closing said discharge opening during movement of said plunger in said opposite direction to its retracted position to produce a sub-atmospheric pressure in said cylinder at the side of said plunger toward said discharge opening sufficient to draw molten casting material through said supply passage into said cylinder through said intake port.

References Cited in the le of this patent UNITED STATES PATENTS 1,954,775 During et al. Apr. 10, 1934 1,960,992 During et al May 29, 1934 1,961,942 Pack June 5, 1934 2,112,342 Lester Mar. 29, 1938 2,112,343 Lester et al. Mar. 29, 1938 2,195,360 Daesen Mar. 26, 1940 2,363,759 Waldie Nov. 28, 1944 42,411,999 Lester Dec. 3, 1946 

